Ruthenium has features, e.g., exhibiting high electrical conductivity, permitting the formation of an electrically conductive oxide, having a high work function, and ensuring excellent etching characteristics and excellent lattice matching with copper and therefore, is attracting attention as a material for a memory electrode such as DRAM, a gate electrode, a copper-wiring seed layer/adhesion layer, etc. In the next-generation semiconductor device, a highly miniaturized and highly three-dimensional design is employed for the purpose of more enhancing the memory capacity or responsiveness. Accordingly, in order to use ruthenium as a material constituting the next-generation semiconductor device, it is required to establish a technique of uniformly forming a ruthenium-containing thin film with a thickness of approximately from a few nanometers to a few tens of nanometers on a three-dimensioned substrate. As the technique for producing a metal thin film on a three-dimensioned substrate, use of a vapor deposition method based on a chemical reaction, such as atomic layer deposition method (ALD method) and chemical vapor deposition method (CVD method), is believed promising. For example, in the case of depositing metallic ruthenium as a next-generation DRAM upper electrode by using this vapor deposition method, a metal oxide such as ZrO2 is used as a capacitor insulating film for the underlying base and therefore, the deposition may be performed under the conditions using an oxidizing gas. In the case of using ruthenium as a next-generation DRAM lower electrode or a copper-wiring seed layer/adhesion layer, titanium nitride, tantalum nitride, etc. is expected to be employed as a barrier metal for the underlying base. When a barrier metal is oxidized at the time of production of a ruthenium-containing thin film, there arises a problem such as deterioration of the barrier performance, defective conduction to a transistor due to rise in the resistance value, and reduction in the responsiveness resulting from an increased interconnection capacity. For the purpose of avoiding such a problem, a material enabling the production of a ruthenium-containing thin film even under the conditions without using an oxidizing gas such as oxygen and ozone is demanded.
In Non-Patent Document 1 and Non-Patent Document 2, (η5-2,4-dimethyl-1-oxa-2,4-pentadienyl)(η5-1,2,3,4,5-pentamethylcyclopentadienyl)ruthenium and (η5-2,4-di-tert-butyl-1-oxa-2,4-pentadienyl)(η5-1,2,3,4,5-pentamethylcyclopentadienyl)ruthenium are described as a compound having a structure similar to that of the ruthenium complex (1a) of the present invention. However, the compounds described in those documents are limited to a complex having an η5-1,2,3,4,5-pentamethylcyclopentadienyl ligand. In addition, the synthesis methods described in those documents are based on a reaction of chloro(η5-1,2,3,4,5-pentamethylcyclopentadienyl)ruthenium with lithium enolate or a reaction of chloro(η5-1,2,3,4,5-pentamethylcyclopentadienyl)ruthenium with an enone derivative and potassium carbonate and are different from the production method of the present invention. Furthermore, those documents are absolutely silent as to using such a complex as a material for the production of a ruthenium-containing thin film.
A cationic ruthenium complex [(η5-cyclopentadienyl)tris(nitrile)ruthenium]+ is useful as a raw material for synthesis of various ruthenium complexes including the ruthenium complex of the present invention. Non-Patent Document 3 describes a method for producing [Ru(η5-C5H5)(MeCN)3][PF6] by irradiating [Ru(η5-C5H5)(η6-C6H6)][PF6] with light in acetonitrile. In addition, Non-Patent Document 4 describes a method for producing [Ru(η5-C5H5)(MeCN)3][PF6] by reacting ruthenocene with aluminum chloride, aluminum, titanium chloride, naphthalene and potassium borofluoride to prepare an η6-naphthalene complex and further reacting acetonitrile therewith.
However, the synthesis methods of a cationic tris(nitrile) complex described in Non-Patent Document 3 and Non-Patent Document 4 have a problem, for example, that equipment for intense ultraviolet irradiation is necessary or an expensive raw material or a large amount of a reactive agent is used, and these methods can hardly be a practical production method excellent in the cost benefit.
As a cationic tris(nitrile)ruthenium complex having a monosubstituted cyclopentadienyl ligand, [(η5-methylcyclopentadienyl)tris(acetonitrile)ruthenium]+ is described in Non-Patent Document 5. In addition, as a cationic ruthenium complex having a pentasubstituted cyclopentadienyl ligand, [(η5-1,2,3,4,5-pentamethylcyclopentadienyl)tris(acetonitrile)ruthenium]+ is described in Non-Patent Document 6. However, there is no report on a cationic tris(nitrile)ruthenium complex having a monosubstituted cyclopentadienyl ligand containing an alkyl group having a carbon number of 2 to 6.
In Non-Patent Document 7, tricarbonyl(η4-1,3,5,7-cyclooctatetraene)ruthenium (Ru(η4-C8H8)(CO)3), tricarbonyl(η4-methyl-1,3,5,7-cyclooctatetraene)ruthenium (Ru(η4-C8H7Me)(CO)3), and tricarbonyl(η4-ethyl-1,3,5,7-cyclooctatetraene)ruthenium (Ru(η4-C8H7Et)(CO)3) are described as a compound capable of producing a metallic ruthenium thin film under the conditions using a reducing gas as the reaction gas. However, the metallic ruthenium thin films produced using these compounds have a high resistivity of 93, 152 and 125 μΩ·cm, respectively, and can be hardly a practical material.
In Non-Patent Document 8, (1-3:5-6-η5-cyclooctadienyl)(η5-2,3,4,5-tetramethylpyrrolyl)ruthenium (Ru(1-3:5-6-η5-C8H11)(η5-NC4Me4)) is described as a compound having a structure similar to that of the ruthenium complex (2) of the present invention. However, the compound described in this document is limited to a complex having a 1-3:5-6-η5-cyclooctadienyl ligand. In addition, the synthesis method described in the document is based on a reaction of di-μ-chloro-(η4-1,5-cyclooctadiene)ruthenium ([Ru(η4-C8H12)Cl2]x) with 2,3,4,5-tetramethylpyrrolyl-lithium and is different from the production method of the present invention. Furthermore, the document is absolutely silent as to using this complex as a material for the production of a ruthenium-containing thin film.
In Non-Patent Document 9, (η5-6-exo-methylcyclohexadienyl)(η5-1,2,3,4,5-pentamethylcyclopentadienyl)ruthenium is described as a compound having a structure similar to that of the ruthenium complex (3) of the present invention, but the compound described in this document is limited to a complex having an η5-1,2,3,4,5-pentamethylcyclopentadienyl ligand. Furthermore, the document is absolutely silent as to using this complex as a material for the production of a ruthenium-containing thin film.